Substrate having a multilayer coat and method for its production

ABSTRACT

The invention relates to a process, in which a body to be coated passes via the entry  1  into the pretreatment stage  2.  This is followed by electrodeposition coating  3  and the baking  4  of the electrodeposition coat. In stage  5  preparation takes place for coating with powder coating material (stage  6 ). In stage  7  drying is carried out with IR irradiation. This is followed by the cooling stage  7.  The powder coating material is applied to the powder coat in stage  9.  Following passage through the intermediate drying stage  10  a protective coat is applied in stage  11  and then is baked in stage  12.  The body is transported out of the unit via the exit  13.

CROSS-REFERENCE TO RELATED APPLICATION

[0001] The present application is a divisional application of U.S. Ser.No. 09/485,797, filed on Apr. 4, 2000, which is a 371 of PCT/EP98/04688,filed on Jul. 25, 1998, which is incorporated herein by reference.

DESCRIPTION

[0002] The invention relates to a substrate provided with a multilayercoating which exhibits a surfacer layer, a colour and/or effectdecorative layer and a protective layer, the surfacer layer beingclosest to the substrate and the protective layer furthest from thesubstrate, the decorative coating material used for the decorative layercomprising a binder from the group “acrylate resins, carboxyl-, epoxy-,and/or hydroxyl-containing binders” or mixtures thereof and comprising acrosslinker from the group “isocyanates, amino resins or TACT” ormixtures thereof and the protective coating material used for theprotective layer being from the group “one-component clearcoats,two-component clear-coats, transparent powder coating materials”, and toa process for preparing such a substrate provided with a multilayercoating.

[0003] A surfacer layer is prepared from a so-called surfacer. Asurfacer is in essence a coating material but one having particularproperties and being applied with a comparatively high layer thickness.The function of a surface layer is to even out disruptive unevennesses(in the micrometer range) on the surface of a substrate, so that thesurface of the substrate need not be subjected to a levellingpretreatment prior to coating. The abovementioned comparatively highlayer thickness of the surfacer is, inter alia, employed for thispurpose. The surfacer may be applied to the material of the substratedirectly or with interposition of a primer and/or adhesion promoter. Inthe former case, when applying the surfacer to a metallic material, itis advisable to use a surfacer having an anti-corrosive action. In thecase of certain surfacers, which have now been surpassedtechnologically, it was necessary to subject the surfacer layer obtainedfollowing application and drying or curing of a surfacer to a levellingsurface treatment, such as sanding. This involved making use of the factthat a surfacer layer is generally less hard and/or easier to work thanthe material of the substrate. Modern surfacers, by contrast, have aself-levelling function. This means that, following application of thesurfacer to a substrate with surface defects, (initial) drying and(initial) crosslinking of the surfacer are all that is required toproduce a surfacer layer whose outer surface is virtually level even inthe micrometer range. In other words, the substrate-side boundarysurface of the resulting surfacer layer forms a complement to thesurface of the substrate, in terms of surface structures in themicrometer range. A decorative layer is formed from a decorative coatingmaterial. A decorative coating material has not only customary coatingsbinders and crosslinkers but also, in particular, colour and/orspecial-effect pigments. Examples of special-effect pigments aremetallic pigments and mica pigments. The decorative layer is essentiallyresponsible for the visual impression to a viewer of the substrateprovided with the multilayer coating. A protective layer is generallyformed from a clearcoat. This clearcoat must have particular propertiesin terms of its behaviour relative to mechanical stress, chemical stressand light stability and in terms of its transmission behaviour, sincethe protective layer is exposed to the environment and is intended, inparticular, to protect the decorative layer. Multilayer coatings of thetype described are used in particular for coating motor vehicle bodiesor parts thereof made from sheet steel or sheet aluminium, but also forcoating plastic mouldings that are employed in the motor vehicle sector.

[0004] The document FR 2 511 617 discloses the application of subsequentlayers to a primer/surfacer layer and only thereafter the curing of themultilayer coating thus formed. This procedure is dubbed “wet on wet”technology. With the processes known to this extent, as far as theprimer/surfacer layer is concerned, a customary aqueous primer/surfaceris employed. It has been found, however, that above certain appliedlayer thicknesses (which are necessary for levelling out substratedefects if in-between sanding is to be avoided) there are instances ofmatting and impaired flow.

[0005] A substrate provided with a multilayer coating and a process forits preparation, of the type specified at the outset, are known from thedocument EP 0 238 037 B1. In this case, an electrodeposition coatingmaterial 15 is used for the primer/surfacer layer. Thiselectro-deposition coating material is initially baked. The decorativelayer and the protective layer are then applied “wet on wet”, it beingpossible for the coating materials used for this purpose to be aqueouscoating materials. Especially in the case of decorative layerscomprising an effect coating material, however, it has been found inaccordance with this document that it is absolutely necessary tointerpose a separating layer between primer and surfacer layer in orderthat the effect of the coating on the finished product satisfies thevisual requirements. The need for a separating layer is a nuisancebecause of the effort required. On grounds of energy consumption, theseparate process step of baking required for the primer/surfacer layeris a nuisance. A further factor is that satisfactory results are onlyachieved when the separating layer is based on organic solvents. This isa nuisance for environmental reasons. If an aqueous coating material isused for the separating layer it is disadvantageous, moreover, thatrapid initial drying of the separating layer prior to applying thesubsequent layers cannot easily be achieved. As a result, the effortand/or the production time is increased to an undesirable extent.

[0006] Against this background, the technical problem on which theinvention is based is to specify a substrate provided with a multilayercoating that can be prepared with little effort and unproblematicenvironmental characteristics, and a process for its preparation.

[0007] To solve this technical problem the invention teaches that thesurfacer layer is formed from a precrosslinkable powder coatingmaterial, the powder-coating surfacer layer having a layer thickness inthe range from 30 μm to 250 μm.—The particular advantages of the use ofa powder coating material for preparing a surfacer layer are, interalia, that it can be done without solvent and that the losses that occurdue to overspray with customary surfacers are avoided since virtuallyall of the non-adhering powder coating material can be recycled. Allcustomary prior art methods are suitable for the application of thepowder coating material. Particular preference is given to applicationby means of electrostatic adhesion, preferably by applying a highvoltage or by frictional charging.

[0008] The coating of substances with powder coating materials is per sea common process. The pulverulent dry coating material is applieduniformly to the substrate to be coated and then the coating material ismelted and baked by heating the substrate. In the context of theinvention, however, and in departure from this customary procedure, thepowder coating material is first of all precrosslinked by heating and isonly baked together with the layers applied subsequently. Therefore,relative to the prior art, a separate process step of baking for thesurfacer layer is omitted. Instead, all layers of coating material arebaked in a common step, leading, surprisingly, to a multilayer coatingwhich satisfies all the requirements. This approach implies aconsiderable simplification of the coating process. The abandonment ofan intermediate baking operation reduces both the capital and operatingcosts. Only a single baking oven need be made available and operated. Asa result, there is also a saving on heating energy. In addition, theoverall operating time for the coating operation is shorter, and so theproductivity of the unit is increased.

[0009] Suitable formulations for the powder coating material are allknown coating-material formulations: for example, those described inEP-509 392, EP-509 393, EP-322 827, EP-517 536, U.S. Pat. No. 5,055,524and U.S. Pat. No. 4,849,283. The powder coating material may inparticular consist of epoxy resins, hybrid systems comprising polyesterresin, and also epoxidized novolaks, and of cross-linking agents,preferably phenolic or amine-type hardeners (curing agents) or bicyclicguanidines, catalysts, fillers and, if desired, auxiliaries andadditives.

[0010] The powder coating materials employed in accordance with theinvention preferably comprise epoxy resins, phenolic crosslinkingagents, catalysts, assistants and also, if desired, auxiliaries andtypical powder additives, and flow aids.

[0011] Suitable epoxy resins are all solid epoxy resins having an epoxyequivalent weight of between 400 and 3000, preferably from 600 to 2000.They principally comprise epoxy resins based on bisphenol A andbisphenol F. Preference is given to epoxidized novolak resins. Thesepreferably have an epoxide equivalent weight of from 500 to 1000.

[0012] The epoxy resins based on bisphenol A and bisphenol F generallyhave a functionality of less than 2, the epoxidized novolak resins afunctionality of greater than 2. Particular preference is given, in thepowder coating materials employed in accordance with the invention, toepoxidized novolak resins having an average functionality in the rangefrom 2.4 to 2.8 and having an epoxide equivalent weight in the rangefrom 600 to 850. In the epoxidized novolak resins, the phenolic hydroxylgroups are etherified with alkyl, acrylic or similar groups. Epoxidegroups are introduced into the molecule by reacting the phenolichydroxyl groups with epichlorohydrins. Starting from novolaks, thisforms the so-called epoxy-novolak. The epoxidized novolaks arestructurally related to bisphenol A resins. Epoxidized novolak resinscan be prepared by epoxidizing novolaks consisting, for example, of 3 to4 phenol nuclei attached to one another via methylene bridges.Alkyl-substituted phenols which are reacted with formaldehyde can alsobe used as novolak resins.

[0013] Suitable epoxy resins are, for example, the products obtainablecommercially under the following names: Epikote 1004, 1055, 3003, 3004,2017 from Shell-Chemie, DER 640, 671, 662, 663 U, 664, 667 from Dow andAraldit GT 6063, 6064, 6084, 6097, 7004, 7220, 7225 from Ciba Geigy.

[0014] Examples of resins suitable as the epoxy-functional binder forthe powder coating material are polyacrylate resins which containepoxide groups and can be prepared by copolymerizing at least oneethylenically unsaturated monomer which contains at least one epoxidegroup in the molecule with at least one further ethylenicallyunsaturated monomer which contains no epoxide group in the molecule, atleast one of the monomers being an ester of acrylic acid or methacrylicacid.

[0015] Polyacrylate resins which contain epoxide groups are known (cf.e.g. EP-A-299 420, DE-B-22 14 650, DE-B-27 49 576, U.S. Pat No.4,091,048 and U.S. Pat. No. 3,781,379).

[0016] Examples of the ethylenically unsaturated monomers which containat least one epoxide group in the molecule are glycidyl acrylate,glycidyl methacrylate and allyl glycidyl ether.

[0017] Examples of ethylenically unsaturated monomers which contain noepoxide group in the molecule are alkyl esters of acrylic andmethacrylic acid which contain 1 to 20 carbon atoms in the alkylradical, especially methyl acrylate, methyl methacrylate, ethylacrylate, ethyl methacrylate, butyl acrylate, butyl methacrylate,2-ethylhexyl acrylate and 2-ethylhexyl methacrylate. Further examples ofethylenically unsaturated monomers which contain no epoxide groups inthe molecule are acids such as, for example, acrylic acid andmethacrylic acid, acid amides, such as acrylamide and methacrylamide,vinylaromatic compounds, such as styrene, methylstyrene and vinyltoluene, nitrites, such as acrylonitrile and methacrylonitrile, vinylhalides and vinylidene halides, such as vinyl chloride and vinylidenefluoride, vinyl esters, such as vinyl acetate, and hydroxyl-containingmonomers, such as hydroxyethyl acrylate and hydroxyethyl methacrylate,for example.

[0018] The polyacrylate resin containing epoxide groups normally has anepoxide equivalent weight of from 400 to 2500, preferably from 500 to1500 and, with particular preference, from 600 to 1200, a number-averagemolecular weight (determined by gel permeation chromatography using apolystyrene standard) of from 1000 to 15,000, preferably from 1200 to7000 and, with particular preference, from 1500 to 5000, and a glasstransition temperature (T_(g)) of from 30 to 80, preferably from 40 to70 and, with particular preference, from 50 to 70° C. (measured by meansof differential scanning calorimetry (DSC)).

[0019] The polyacrylate resin containing epoxide groups can be preparedby generally well-known methods, by means of free-radical additionpolymerization.

[0020] Examples of suitable hardeners for the polyacrylate resin whichcontains epoxide groups are polyanhydrides of polycarboxylic acids or ofmixtures of polycarboxylic acids, especially polyanhydrides ofdicarboxylic acids or of mixtures of dicarboxylic acids.

[0021] Polyanhydrides of this kind can be prepared by removing waterfrom the polycarboxylic acid or from the mixture of polycarboxylicacids, with in each case two carboxyl groups being reacted to form oneanhydride group. Preparation processes of this kind are well known andso need not be discussed further.

[0022] For curing the epoxy resins, the powder coating material which isto this extent used in accordance with the invention comprises phenolicor amine-type hardeners. It is also possible to employ bicyclicguanidines.

[0023] In this context, for example, any desired phenolic resin can beused provided that it has the methylol functionality required forreactivity. Preferred phenolic resins are reaction products of phenol,substituted phenols and bisphenol A with formaldehyde that are preparedunder alkaline conditions. Under such conditions, the methylol group islinked to the aromatic ring in either ortho or para position. Asphenolic crosslinking agents it is particularly preferred to employhydroxyl-containing bisphenol A resins or bisphenol F resins having ahydroxy equivalent weight in the range from 180 to 600 and, withparticular preference, in the range from 180 to 300.

[0024] Phenolic crosslinking agents of this kind are prepared byreacting bisphenol A or bisphenol F with glycidyl-containing components,such as the diglycidyl ether of bisphenol A, for example. Phenoliccrosslinking agents of this kind are obtainable, for example, under thecommercial designation DEH 81, DEH 82 and DEH 87 from Dow, DX 171 fromShell-Chemie and XB 3082 from Ciba Geigy.

[0025] In this context, the epoxy resins and phenolic cross-linkingagents are employed in a ratio such that the number of epoxide groups tothe number of phenolic OH groups is approximately 1:1.

[0026] Such powder coating materials, used in accordance with theinvention, comprise one or more suitable catalysts for epoxy resincuring. Suitable catalysts are phosphonium salts of organic or inorganicacids, imidazole and imidazole derivatives, quaternary ammoniumcompounds, and amines. The catalysts are generally employed inproportions of from 0.001% by weight to about 10% by weight, based onthe overall weight of the epoxy resin and the phenolic crosslinkingagent.

[0027] Examples of suitable phosphonium salt catalysts areethyltriphenylphosphonium iodide, ethyltriphenylphosphonium chloride,ethyltriphenylphosphonium thiocyanate, ethyltriphenylphosphoniumacetate-acetic acid complex, tetrabutylphosphonium iodide,tetrabutylphosphonium bromide and tetrabutylphosphonium acetate-aceticacid complex. These and other suitable phosphonium catalysts aredescribed, for example, in U.S. Pat. No. 3,477,990 and U.S. Pat. No.3,341,580.

[0028] Examples of suitable imidazole catalysts are 2-styryl-imidazole,1-benzyl-2-methylimidazole, 2-methylimidazole and 2-butylimidazole.These and other imidazole catalysts are described, for example, inBelgian Patent No. 756,693.

[0029] In some cases, customary commercial phenolic crosslinking agentsalready include catalysts for epoxy resin crosslinking.

[0030] Powder coating materials based on carboxyl-containing polyestersand on epoxy-containing crosslinking agents of low molecular mass areknown in large numbers and are described, for example, in EP-A-389 926,EP-A-371 522, EP-A-326 230, EP-B-110 450, EP-A-110 451, EP-B-107 888,U.S. Pat. No. 4,340,698, EP-B-119 164, WO 87/02043 and EP-B-10 805.

[0031] Also particularly suitable are powder coating materials inaccordance with DE 43 30 404.4 A1, which are characterized in that theycomprise as film-forming material A) 35.0-92.2% by weight ofcarboxyl-containing polyesters having an acid number of 10-150 mg ofKOH/g, B) 0.8-20.1% by weight of epoxy-containing curing agents of lowmolecular mass, C) 3.7-49.3% by weight of epoxy-containing polyacrylateresins having an epoxide equivalent weight of 350-2000 and D) 0.5-13.6%by weight of low molecular mass di- and/or polycarboxylic acids and/ordi- and/or polyanhydrides, the sum of the proportions by weight of A),B), C) and D) in each case being 100% by weight and the ratio of theepoxide groups of the powder coating materials to the sum of thecarboxyl and anhydride groups of the powder coating materials being0.75-1.25:1.

[0032] The carboxyl-containing polyesters used as component A) have anacid number in the range of 10-150 mg of KOH/g, preferably in the rangeof 30-100 mg of KOH/g. The hydroxyl number of the polyester resinsshould be <30 mg of KOH/g. It is preferred to employ polyesters having acarboxy functionality of >2. The polyesters are prepared by thecustomary methods (compare e.g. Houben Weyl, Methoden der OrganischenChemie, 4^(th) edition, Volume 14/2, Georg Thieme Verlag, Stuttgart1961).

[0033] Suitable carboxylic acid components for preparing the polyestersare aliphatic, cycloaliphatic and aromatic di- and polycarboxylic acids,such as phthalic, terephthalic, isophthalic, trimellitic, pyromellitic,adipic, succinic, glutaric, pimelic, suberic, cyclohexanedicarboxylic,azelaic and sebacic acid and the like. These acids can in this contextalso be employed in the form of their esterifiable derivatives (e.g.anhydrides) or their transesterifiable derivatives (e.g. dimethylesters).

[0034] Suitable alcohol components for preparing the carboxyl-containingpolyesters A) are the commonly employed di- and/or polyols, examplesbeing ethylene glycol, 1,2-propanediol and 1,3-propanediol, butanediols,diethylene glycol, triethylene glycol, tetraethylene glycol,1,6-hexanediol, neopentyl glycol, 1,4-dimethylolcyclohexane, glycerol,trimethylolethane, trimethylolpropane, pentaerythritol,ditrimethylolpropane, dipentaerythritol, diglycerol, and the like.

[0035] The polyesters thus obtained can in this context be employedindividually or as a mixture of different polyesters. The polyesterssuitable as component A) generally have a glass transition temperatureof above 30° C.

[0036] Examples of suitable customary commercial polyesters are theproducts obtainable commercially under the following trade names:Crylcoat 314, 340, 344, 2680, 316, 2625, 320, 342 and 2532 from UCB,Drogenbos, Belgium; Grilesta 7205, 7215, 72-06, 72-08, 72-13, 72-14,73-72, 73-93 and 7401 from Ems-Chemie; Neocrest P670, P671, P672, P678,P662 from ICI and Uralac P2400, Uralac P3400 and Uralac P5000 from DSM.

[0037] Unsaturated, carboxyl-containing polyester resins are alsosuitable as acidic polyester component A). They are obtained bypolycondensation of, for example, maleic acid, fumaric acid or otheraliphatic or cycloaliphatic dicarboxylic acids having an ethylenicallyunsaturated double bond, alone or together with saturated polycarboxylicacids, as polycarboxylic acid component. The unsaturated groups can alsobe introduced into the polyester through the alcohol component, e.g.through trimethylolpropane monoallyl ether.

[0038] The powder coating materials used to this extent in accordancewith the invention comprise as component B) 0.8-20.1% by weight ofepoxy-containing curing agents of low molecular mass. An example of aparticularly suitable epoxy-containing curing agent of low molecularmass is triglycidyl isocyanurate (TGIC). TGIC is obtainablecommercially, for example, under the designation Araldit PT 810(manufacturer: Ciba Geigy). Other suitable epoxy-containing curingagents of low molecular mass are 1,2,4-triglycidyltriazoline-3,5-dione,diglycidyl phthalate, and the diglycidyl ester of hexahydrophthalicacid.

[0039] By epoxy-containing polyacrylate resins (component C) are meantpolymers preparable by copolymerizing at least one ethylenicallyunsaturated monomer which contains at least one epoxide group in themolecule with at least one further ethylenically unsaturated monomerwhich contains no epoxide group, at least one of the monomers being anester of acrylic acid or of methacrylic acid.

[0040] Polyacrylate resins which contain epoxide groups are known (cf.e.g. EP-A-299 420, DE-B-22 14 650, U.S. Pat. No. 4,091,048 and U.S. Pat.No. 3,781,379).

[0041] Examples of ethylenically unsaturated monomers which contain atleast one epoxide group in the molecule are glycidyl acrylate, glycidylmethacrylate and allyl glycidyl ether.

[0042] Examples of ethylenically unsaturated monomers which contain noepoxide group in the molecule are alkyl esters of acrylic andmethacrylic acid which contain 1 to 20 carbon atoms in the alkylradical, especially methyl acrylate, methyl methacrylate, ethylacrylate, ethyl methacrylate, n-butyl acrylate, isobutyl acrylate,t-butyl acrylate and the corresponding methacrylates, 2-ethylhexylacrylate and 2-ethylhexyl methacrylate. Further examples ofethylenically unsaturated monomers which contain no epoxide groups inthe molecule are acids such as, for example, acrylic acid andmethacrylic acid, acid amides, such as acrylamide and methacrylamide,vinylaromatic compounds, such as styrene, methylstyrene andvinyltoluene, nitrites, such as acrylonitrile and methacrylonitrile,vinyl halides and vinylidene halides, such as vinyl chloride andvinylidene fluoride, vinyl esters, such as vinyl acetate and vinylpropionate, and hydroxyl-containing monomers, such as hydroxyethylacrylate and hydroxyethyl methacrylate, for example.

[0043] The polyacrylate resin containing epoxide groups (component C)has an epoxide equivalent weight of from 350 to 2000. Theepoxy-containing polyacrylate resins normally have a number-averagemolecular weight (determined by gel permeation chromatography using apolystyrene standard) of from 1000 to 15,000 and a glass transitiontemperature (T_(g)) of 30-80 (measured by means of differential scanningcalorimetry (DSC)).

[0044] The epoxy-containing acrylate resin can be prepared by generallywell-known methods, by free-radical addition polymerization. Suchepoxy-containing polyacrylate resins are obtainable commercially, forexample, under the designation Almatex PD 7610 and Almatex PD 7690(manufacturer: Mitsui Toatsu).

[0045] As binders, powder coating materials used to this extent inaccordance with the invention include as component D) 0.5-13.6% byweight of low molecular mass di- and/or polycarboxylic acids and/or di-and/or polyanhydrides. It is preferred as component D) to use saturated,aliphatic and/or cycloaliphatic dicarboxylic acids, such as glutaric,adipic, pimelic, suberic, azelaic, cyclohexanedicarboxylic, sebacic,malonic, dodecanedioic and succinic acids. Also suitable as component D)are aromatic di- and polycarboxylic acids, such as phthalic,terephthalic, isophthalic, trimellitic and pyromellitic acids, also ofcourse in the form of their anhydrides where they exist. Particularpreference is given to dodecanedioic acid (=1,10-decanedicarboxylicacid) for use as component D).

[0046] The amounts of the powder coating components A) to D) are chosensuch that the ratio of the epoxide groups of B) and C) to the sum of thecarboxyl and anhydride groups of A) and D) is 0.75-1.25:1. This ratio ispreferably 0.9-1.1:1.

[0047] The powder coating material can contain from 50 to 90%,preferably from 60 to 80% by weight of binders and from 10 to 50% byweight, preferably from 20 to 40% by weight of fillers. Suitable fillersare crystalline modifications of silica functionalized with glycidylgroups. They are normally employed in the stated range of from 10 to 50%by weight, based on the overall weight of the powder coating material.In certain cases, however, proportions of filler of more than 50% byweight are also possible. The crystalline modifications of silicainclude quartz, cristobalite, tridymite, keatite, stishovite,melanophlogite, coesite and fibrous silica. The crystallinemodifications of silica are functionalized with glycidyl groups, theglycidyl-group functionalization being obtained by means of a surfacetreatment. The silica modifications concerned comprise, for example,those based on quartz, cristobalite and fused silica that are preparedby treating the crystalline silica modifications with epoxysilanes. Theglycidyl-functionalized silica modifications are obtainablecommercially, for example, under the designation Silbond® 600 EST andSilbond® 6000 EST (manufacturer: Quarzwerke GmbH) and are prepared byreacting crystalline silica modifications with epoxysilanes. The powdercoating materials advantageously include from 10 to 40% by weight, basedon the overall weight of the powder coating material, ofglycidyl-functionalized crystalline silica modifications.

[0048] The powder coating material may also comprise further inorganicfillers, examples being titanium oxide, barium sulphate andsilicate-based fillers, such as talc, kaolin, magnesium silicates,aluminium silicates, mica and the like, for example. The powder coatingmaterials may additionally comprise, if desired, auxiliaries andadditives. Examples thereof are levelling agents, flow aids anddegassing agents, such as benzoin, for example.

[0049] The powder coating materials are prepared by known methods (cf.e.g. product information from BASF Lacke+Farben AG, “Pulverlacke”[Powder coating materials], 1990) by homogenization and dispersion bymeans, for example, of an extruder, screw compounder and the like.Following preparation of the powder coating material, it is adjusted tothe desired particle size distribution by milling and, if desired, bysieving and classifying. To promote non-destructive expulsion of gas itis also possible to add degassing agents to the powder coating material,preferably benzoylphenylmethanol (benzoin) in concentrations of up to 2%by weight, preferably 0.4% by weight.

[0050] For the decorative layer it is possible to use all common aqueousdecorative coating materials from the stated group. Reference is made inthis context, for example, to the documents EP 89 497 or EP 38 127.Suitable crosslinkers are isocyanates, amino resins and/or TACT(tris[alkoxycarbonylamino]triazines, especially as described in thedocument U.S. Pat. No. 5,084,541).

[0051] Preference is given to a decorative coating material whichcomprises an aqueous polymer dispersion comprising (i) an acrylatepolymer based on from 30 to 60% by weight of C₁-C₈-alkyl (meth)acrylatemonomers, from 30 to 60% by weight of vinylaromatic monomers and from0.5 to 10% by weight of (meth)acrylic acid and (ii) a non-associativethickener which comprises an acrylate copolymer based on C₁-C₆-alkyl(meth)acrylate and (meth)acrylic acid.

[0052] As C₁-C₈-alkyl (meth)acrylate monomer units the acrylate polymerof component (i) that is employed can comprise the linear andbranched-chain derivatives, preference being given to methyl(meth)acrylate, ethyl (meth)acrylate, n-propyl and isopropyl(meth)acrylate, n-butyl and isobutyl (meth)acrylate and 2-ethylhexyl(meth)acrylate. Further monomers which may be present include(meth)acrylamide monomers and derivatives thereof.

[0053] Vinylaromatic monomers present as monomer units in the acrylatepolymer of component (i) can be, for example, styrene, α-alkylstyrenesand vinyltoluene.

[0054] The acrylate polymer can be prepared by processes known from theprior art, such as emulsion polymerization. The acrylate polymer ispreferably employed in the form of a dispersion. During the preparationprocess, the quantitative proportion between the monomers and the wateris adjusted preferably such that the resulting dispersion has a solidscontent of from 30 to 60% by weight, preferably from 35 to 60% byweight, and can be employed directly for preparing the basecoatingcomposition. A particularly suitable acrylate polymer is obtainablecommercially as an aqueous dispersion under the designation Acronal 290D (BASF AG; Ludwigshafen).

[0055] To prepare a dispersion of the acrylate polymer it is preferred,as emulsifier, to employ an anionic emulsifier alone or in a mixturewith others.

[0056] Examples of anionic emulsifiers are the alkali metal salts ofsulphuric monoesters of alkylphenols or alcohols, and also the sulphuricmonoesters of ethoxylated alkylphenols or ethoxylated alcohols,preferably the alkali metal salts of the sulphuric monoester of anonylphenol reacted with from 4 to 5 mol of ethylene oxide per mole,alkyl- or arylsulphonates, sodium lauryl sulphate, sodium laurylethoxylate sulphate and secondary sodium alkanesulphonates whose carbonchain contains 8-20 carbon atoms. The amount of the anionic emulsifieris from 0.1 to 5.0% by weight, based on the monomers, preferably from0.5 to 3.0% by weight. In order to increase the stability of the aqueousdispersions it is also possible in addition to employ a nonionicemulsifier of the type of an ethoxylated alkylphenol or fattyalcohol—for example, an adduct of 1 mol of nonylphenol and from 4 to 30mol of ethylene oxide—in a mixture with the anionic emulsifier.

[0057] The glass transition temperature of the acrylate polymerpreferably lies between 15° C. and 35° C. and, with particularpreference, between 20° C. and 25° C.

[0058] The acrylate polymer employed preferably has a number-averagemolecular mass (determination: by gel permeation chromatography withpolystyrene as standard) of from 200,000 to 2,000,000, preferably from300,000 to 1,500,000.

[0059] As thickener component (ii) in the decorative coating materialuse is made, in accordance with the invention, of acrylate copolymershaving non-associative groups, which comprise C₁-C₆-alkyl (meth)acrylateand (meth)acrylic acid as monomer units. A preferred copolymer comprisesas its monomer units (meth)acrylic acid and at least two differentC₁-C₆-alkyl (meth)acrylate monomers. In the copolymer the (meth)acrylicacid is present preferably in amounts of from 40% by weight to 60% byweight and, with particular preference, from 46% by weight to 55% byweight, based on the amount of the copolymer as a whole. The C₁-C₆-alkyl(meth)acrylate monomer I is preferably present in amounts of from 30% byweight to 50% by weight, in particular from 36% by weight to 46% byweight, and the (meth)acrylate polymer II preferably in amounts of from1% by weight to 10% by weight, in particular from 2% by weight to 8% byweight, based in each case on the amount of the copolymer as a whole.The rheological auxiliary is intended to give the decorative coatingmaterial the desired viscosity, especially at the generally alkaline pHthat is employed. A particularly preferred thickener is—if in dispersionform—highly mobile and thickens at a neutral or basic pH. The acrylatecopolymer is suitably employed as a finished dispersion. As emulsifiers,such dispersions preferably contain fatty alcohol alkoxylates,especially C₈-C₂₂ fatty alcohol ethoxylates. A particularly suitableacrylate copolymer dispersion is obtainable commercially under thedesignation Viscalex HV 30 (Allied Corporation, Great Britain).

[0060] In the decorative coating material used, the thickener ispreferably present in an amount of from 0.5 to 5.0% by weight, inparticular from about 0.3 to 1.5% by weight, based on the solidscontent. The thickener is customarily employed as a dispersion having aconcentration of from 5 to 45% by weight, preferably from 7 to 35% byweight.

[0061] The decorative coating material may also include furtherthickeners and/or Theological auxiliaries, such as ionicphyllosilicates, xanthan gum, diurea compounds, polyurethane thickeners,bentonite, waxes, and wax copolymers.

[0062] As auxiliary binders, the decorative coating material may alsoinclude epoxy-functional and/or carboxyl-functional constituents, suchas customary glycidyl compounds, examples being glycidyl acrylate orglycidyl methacrylate. Examples of suitable carboxyl-functionalcrosslinkers are carboxylic acids, especially saturated, straight-chain,aliphatic dicarboxylic acids having 3 to 20 carbon atoms in themolecule, preference being given to the use of dodecane-1,12-dioic acid.

[0063] As a further auxiliary binder, polyvinyl alcohol may also beemployed. It has been found that by adding polyvinyl alcohol in anamount of up to 10% by weight, preferably from 1 to 5% by weight, it ispossible to improve the compatibility with the protective coatingmaterials that are applied to the decorative coating material. Polyvinylalcohol has a solvent-repelling effect, so that any solvent present inthe protective coating material, or other components, are unable—owingto the repelling action of the polyvinyl alcohol—to penetrate thedecorative coating material and alter the colour.

[0064] As further crosslinkers it is possible to employ the crosslinkersknown in the paints sector, such as melamine resins, which are able toreact with free OH groups.

[0065] In addition to the polymers described above, the decorativecoating material may also include further compatible water-dilutableresins, such as amino resins, polyesters, polyurethanes and alsoacrylicized polyurethanes and urethanized acrylates, which serve asadditives for achieving particular paints properties, such as improvedadhesion, or, in general, as grinding resins for pigments.

[0066] The auxiliary binder and/or the crosslinker can be employed in anamount of up to 10% by weight, in particular from 0.5 to 10% by weight.

[0067] The decorative coating material employed generally has a solidscontent of from about 15 to 60% by weight. The solids content varieswith the type of effect of the decorative coating material. For metalliccoating materials, for example, it is preferably from 12 to 25% byweight. For solid-colour coating materials it is higher, preferably from14 to 45% by weight.

[0068] In order to neutralize components (i) and (ii) it is possible toemploy ammonia and/or amines (especially alkylamines), amino alcoholsand cyclic amines, such as di- and triethylamine, aminomethylpropanol,dimethylaminoethanolamine, diisopropanolamine, morpholine,N-alkylmorpholine. For neutralization, readily volatile amines arepreferred. The aqueous coating composition is usually adjusted to a pHof between 6 and 9, preferably from 7 to 8.5.

[0069] The decorative coating material can comprise organic solvents inan amount of up to 15% by weight. Examples of suitable organic solventsare naphthalenes, petroleum spirits and alcohols. As further liquidcomponents the basecoats of the invention may include alkylene glycols,such as ethylene glycol, propylene glycol, butylene glycol,1,4-butanediol, 1,6-hexanediol, neopentyl glycol and other diols, suchas dimethylolcyclohexane.

[0070] As pigments, the decorative coating material may includecustomary pigments employed for coating car bodies, such as, forexample, special-effect pigments and also organic and inorganic colourpigments. Examples of suitable special-effect pigments are customarycommercial aluminium bronzes, the aluminium bronzes chromated inaccordance with DE-A 36 36 183, customary commercial stainless-steelbronzes and also other customary metal platelets and metal flakepigments, and nonmetallic special-effect pigments, such as pearl lustrepigments and interference pigments, for example. Examples of suitableinorganic colour pigments are titanium dioxide, iron oxides and carbonblack and the like. Examples of organic colour pigments are Indanthreneblue, Cromophthal red, Irgazine orange, Sicotrans yellow, Heliogen greenand the like. It is also possible for anticorrosive pigments such aszinc phosphate, to be present, In addition, the decorative coatingmaterial may also contain fillers customary in the field of paintchemistry. These include silica, magnesium silicate, talc, titaniumdioxide and barium sulphate. The proportion of pigments and fillers inthe decorative coating material may amount in total to from 3 to 25% byweight, based on the solids content. The pigment can be added in anydesired form, for example as an aqueous slurry or as a paste. Thepigments may be dispersed, for example, with a grinding resin, such asan auxiliary binder, dispersing auxiliary or water. In the case ofsolid-colour coating materials it is preferred to slurry the pigments indispersing auxiliary and water. Where aluminium and/or flakes areemployed they are, if desired, slurried in solvent and, if appropriate,in a mixture of water and wetting agent or are dispersed in theprincipal binder or in another, auxiliary binder. The amount ofcomponent (i) can vary depending on the pigment employed. Where thepigments are organic and/or inorganic colour pigments, component A ispreferably present in an amount of from 25 to 50% by weight, based onthe solids content. Where the pigments are special-effect pigments,component A is preferably present in an amount of from 15 to 30% byweight based on the solids content.

[0071] As a further component the decorative coating material mayinclude film-forming auxiliaries. Suitable film-forming auxiliaries aredialkyl dicarboxylates, 1,2-propylene glycol, high-boiling petroleumspirits, and naphthalenes, having a boiling point of more than 100° C.,preferably more than 140° C. The decorative coating material may also,if desired, contain further auxiliaries and additives. Examples of theseare catalysts, assistants, antifoams, dispersing auxiliaries, wettingagents, preferably carboxy-functional dispersants, antioxidants, UVabsorbers, free-radical scavengers, levelling agents, biocides and/orwater-retention agents.

[0072] If desired, prior to application to the surfacer layer, water canbe added to the decorative coating material in order to adjust thesolids content, or solvents or rheological auxiliaries can be added inorder to establish the performance properties, and also, if desired, abase can be added to regulate the pH. If the viscosity is still notwithin the desired range, further rheological auxiliary (ii) or furtherthickener, if appropriate in an amount of from 0.001 to 0.006% byweight, based on the solids content, can be added.

[0073] In addition, conventional powder coating materials are alsosuitable as the decorative coating material or colour-imparting layer ofcoating material.

[0074] Suitable aqueous protective coating materials are all commontransparent coating materials. Particular preference is given to the useof the following protective coating materials.

[0075] A first preferred protective coating material is an aqueouspowder coating dispersion and is characterized in that the aqueouspowder coating dispersion can be prepared by subjecting an aqueousdispersion of a powder coating material having a glass transitiontemperature of from 20 to 90° C., preferably from 40 to 70° C., aviscosity of from 10 to 1000 mPas, preferably from 50 to 300 mPas, at ashear rate of 500 s⁻¹ and a solids content of from 10 to 50%, preferablyfrom 20 to 40%, to a grinding process while observing a temperature offrom 0 to 60° C., preferably from 5 to 35° C. The specific energy inputduring the grinding process is preferably from 20 to 500 Wh/kg, inparticular from 50 to 250 Wh/kg.

[0076] In terms of chemical composition, this aqueous powder coatingdispersion is constructed, for example, such that it consists of a solidpulverulent component A and of an aqueous component B, component A beinga powder coating material comprising a) at least one epoxy-containingbinder having a content of from 30 to 45%, preferably from 30 to 35% ofglycidyl-containing monomers with or without a content of vinylaromaticcompounds, preferably styrene, b) at least one crosslinking agent,preferably straight-chain, aliphatic dicarboxylic acids and/orcarboxy-functional polyesters, and c) if desired, catalysts, assistants,additives typical of powder coating materials, such as degassing agents,levelling agents, UV absorbers, free-radical scavengers andantioxidants, and component B being an aqueous dispersion comprising a)at least one nonionic thickener and b) if desired, catalysts,assistants, antifoams, dispersing auxiliaries, wetting agents,preferably carboxy-functional dispersants, antioxidants, UV absorbers,free-radical scavengers, small amounts of solvent, levelling agents,biocides and/or water-retention agents.

[0077] Examples of suitable epoxy-functional binders for component A arepolyacrylate resins which contain epoxide groups and can be prepared bycopolymerizing at least one ethylenically unsaturated monomer whichcontains at least one epoxide group in the molecule with at least onefurther ethylenically unsaturated monomer which contains no epoxidegroup in the molecule, at least one of the monomers being an ester ofacrylic acid or methacrylic acid. Polyacrylate resins of this kindcontaining epoxide groups are known, for example, from EP-A-299 420,DE-B-22 14 650, DE-B-27 49 576, U.S. Pat. No. 4,091,048 and U.S. Pat.No.3,781,379.

[0078] Examples of ethylenically unsaturated monomers which contain noepoxide group in the molecule are alkyl esters of acrylic andmethacrylic acid which contain 1 to 20 carbon atoms in the alkylradical, especially methyl acrylate, methyl methacrylate, ethylacrylate, ethyl methacrylate, butyl acrylate, butyl methacrylate,2-ethylhexyl acrylate and 2-ethylhexyl methacrylate. Further examples ofethylenically unsaturated monomers which contain no epoxide groups inthe molecule are acid amides, such as acrylamide and methacrylamide,vinylaromatic compounds, such as styrene, methylstyrene andvinyltoluene, nitrites, such as acrylonitrile and methacrylonitrile,vinyl halides and vinylidene halides, such as vinyl chloride andvinylidene fluoride, vinyl esters, such as vinyl acetate, andhydroxyl-containing monomers, such as hydroxyethyl acrylate andhydroxyethyl methacrylate, for example.

[0079] The polyacrylate resin containing epoxide groups normally has anepoxide equivalent weight of from 400 to 2500, preferably from 420 to700, a number-average molecular weight (determined by gel permeationchromatography using a polystyrene standard) of from 2000 to 20,000,preferably from 3000 to 10,000 and a glass transition temperature(T_(g)) of from 30 to 80, preferably from 40 to 70 and, with particularpreference, from 40 to 60° C. (measured by means of differentialscanning calorimetry (DSC)). Very particular preference is given toabout 50° C. It is also possible to employ mixtures of two or moreacrylate resins.

[0080] The polyacrylate resin containing epoxide groups can be preparedby generally well-known methods, by means of addition polymerization.

[0081] Suitable crosslinkers are carboxylic acids, especially saturatedstraight-chain aliphatic dicarboxylic acids having 3 to 20 carbon atomsin the molecule. It is very particularly preferred to employdecane-1,12-dicarboxylic acid. For modifying the properties of thefinished transparent powder coating materials it is also possible ifdesired to employ other carboxyl-containing crosslinkers. Examplesthereof which may be mentioned are saturated branched or unsaturatedstraight-chain di- and polycarboxylic acids and also polymers havingcarboxyl groups.

[0082] Also suitable, furthermore, are components A which comprise anepoxy-functional crosslinker and an acid-functional binder.

[0083] Examples of suitable acid-functional binders are acidicpolyacrylate resins which can be prepared by copolymerizing at least oneethylenically unsaturated monomer which contains at least one acid groupin the molecule with at least one further ethylenically unsaturatedmonomer which contains no acid groups in the molecule.

[0084] The binder containing epoxide groups or the crosslinkercontaining epoxide groups and the carboxyl crosslinker or theCOOH-binder are normally employed in an amount such that there are from0.5 to 1.5, preferably from 0.75 to 1.25 equivalents of carboxyl groupsper equivalent of epoxide groups. The amount of carboxyl groups presentcan be determined by titration with an alcoholic KOH solution.

[0085] The binder contains vinylaromatic compounds, especially styrene.To limit the risk of cracking, however, the content is not above 35% byweight. Preference is given to from 10 to 25% by weight.

[0086] The components A may include one or more suitable catalysts forepoxy resin curing. Suitable catalysts are phosphonium salts of organicor inorganic acids, quaternary ammonium compounds, amines, imidazole andimidazole derivatives. The catalysts are generally employed inproportions of from 0.001% by weight to about 2% by weight, based on theoverall weight of the epoxy resin and of the crosslinking agent.

[0087] Examples of suitable phosphonium catalysts areethyltriphenylphosphonium iodide, ethyltriphenylphosphonium chloride,ethyltriphenylphosphonium thiocyanate, ethyltriphenylphosphoniumacetate-acetic acid complex, tetrabutylphosphonium iodide,tetrabutylphosphonium bromide and tetrabutylphosphonium acetate-aceticacid complex. These and other suitable phosphonium catalysts aredescribed, for example, in U.S. Pat. No. 3,477,990 and U.S. Pat. No.3,341,580.

[0088] Examples of suitable imidazole catalysts are 2-styrylimidazole,1-benzyl-2-methylimidazole, 2-methylimidazole and 2-butylimidazole.These and other imidazole catalysts are described, for example, inBelgian Patent No. 756,693.

[0089] In addition, the components A may also if desired compriseauxiliaries and additives. Examples thereof are levelling agents,antioxidants, UV absorbers, free-radical scavengers, flow aids anddegassing agents, such as benzoin, for example. Suitable levellingagents are those based on polyacrylates, polysiloxanes and/or fluorinecompounds. Antioxidants which can be employed are reducing agents, suchas hydrazides and phosphorus compounds, and also free-radicalscavengers, e.g. 2,6-di-tert-butylphenol derivatives. UV absorbers whichcan be used are preferably triazines and benzotriphenol. Free-radicalscavengers which can be employed are preferably2,2,6,6-tetramethylpiperidine derivatives.

[0090] As a further constituent, the aqueous component B of the powdercoating dispersion contains at least one nonionic thickener a). It ispreferred to employ nonionic associative thickeners a). Structuralfeatures of such associative thickeners a) are: aa) a hydrophilicframework, which ensures sufficient solubility in water, and ab)hydrophobic groups which are capable of associative interaction in anaqueous medium.

[0091] Examples of hydrophobic groups employed are long-chain alkylradicals, such as dodecyl, hexadecyl or octadecyl radicals, or alkarylradicals, such as octylphenyl or nonylphenyl radicals, for example.Hydrophilic frameworks employed are preferably polyacrylates, celluloseethers or, with particular preference, polyurethanes, which contain thehydrophobic groups as polymer units.

[0092] Very particular preference is given as hydrophilic frameworks topolyurethanes which comprise polyether chains as units, preferablycomprising polyethylene oxide. In connection with the synthesis of suchpolyether polyurethanes the di- and/or polyisocyanates, preferablyaliphatic diisocyanates, and, with particular preference, unsubstitutedor alkyl-substituted 1,6-hexamethylene diisocyanate, serve to link thehydroxyl-terminated polyether units to one another and to link thepolyether units to the hydrophobic end-group units, which may, forexample, be monofunctional alcohols and/or amines having the alreadymentioned long-chain alkyl radicals or aralkyl radicals.

[0093] Component B may also include catalysts, levelling agents,antioxidants, UV absorbers, free-radical scavengers and wetting agents.Essentially, suitable substances here are those already listed forcomponent A. It is also possible for assistants, antifoams, dispersionauxiliaries, biocides, solvents and neutralizing agents to be added tocomponent B. Suitable antifoams are preferably modified polysiloxanes.Dispersion auxiliaries are, for example, preferably ammonium or metalsalts of polycarboxylates. Neutralizing agents which can be used areamines, ammonia and metal hydroxides.

[0094] Component A is prepared by known methods (cf. e.g. productinformation from BASF Lacke+Farben AG, “Pulverlacke” [Powder coatings],1990) by homogenization and dispersion by means, for example, of anextruder, screw compounder and the like. Following preparation of thepowder coating materials, they are prepared for dispersion by grindingand, if appropriate, by sieving and classifying. The aqueous transparentpowder coating dispersion can then be prepared from the powder by wetgrinding or by stirring in dry-ground powder coating material. Wetgrinding is particularly preferred. The resulting average particle sizelies between 1 and 25 μm, preferably below 20 μm and, very preferably,from 3 to 10 μm. It is important that during the grinding process thedispersion contains only small amounts of solvent. It may therefore benecessary under certain circumstances to free the mill from solventresidues before beginning the grinding process.

[0095] Before or after wet grinding and/or the introduction of componentA into the water it is possible to add to the dispersion from 0 to 5% byweight of an antifoam mixture, an ammonium and/or alkali metal salt, acarboxyl-functional or nonionic dispersion auxiliary, wetting agentand/or thickener mixture and also the other additives. Antifoam,dispersing auxiliary, wetting agent and/or thickener are preferablydispersed first of all in water. Then small portions of component A arestirred in. Subsequently, antifoam, dispersing auxiliary, thickener andwetting agent are incorporated again by dispersion. Finally, component Ais stirred in again in small portions. Adjustment of the pH takes placepreferably using ammonia or amines. In this context the pH may first ofall rise, to form a strongly basic dispersion. However, the pH fallsagain over several hours or days to the values specified above. Thepowder coating dispersions can be applied to the decorative layer usingthe methods known from liquid coatings technology. In particular, theycan be applied by means of spraying processes. Also suitable areelectrostatically assisted high-speed rotation or pneumaticapplications. The transparent powder coating dispersion applied to thedecorative layer is in most cases flashed off prior to baking. Thisjudiciously takes place first at room temperature and then at slightlyelevated temperature. In general the elevated temperature is from 40 to70° C., preferably from 50 to 65° C. Flashing off is carried out for 2to 10 minutes, preferably from 4 to 8 minutes, at room temperature. Atelevated temperature, flashing off is again carried out for the sameperiod of time. With a protective coating material of the type describedabove it is possible to achieve layer thicknesses of from 30 to 50 μm.

[0096] A second preferred protective coating material is a two-componentclearcoat comprising (1) a hydroxy-functional binder or a mixture ofhydroxy-functional binders, (2) tris(alkoxycarbonylamino)triazine or amixture of tris(alkoxycarbonylamino)triazines, and (3) freepolyisocyanates or a mixture of free polyisocyanates.

[0097] Suitable hydroxy-functional binders are preferably those based onhydroxy-functional polyacrylates, hydroxy-functional polyesters and/orhydroxy-functional polyurethanes.

[0098] It is preferred to employ polyacrylate resins which have hydroxylnumbers of from 40 to 240, preferably from 60 to 210 and, with veryparticular preference, from 100 to 200, acid numbers of from 0 to 35,preferably from 0 to 23, and, with very particular preference, from 3.9to 15.5, glass transition temperatures of from −35 to +70° C.,preferably from −20 to +40° C. and, with very particular preference,from −10 to +15° C. and number-average molecular weights of from 1500 to30,000, preferably from 2000 to 15,000 and, with very particularpreference, from 2500 to 5000.

[0099] The glass transition temperature of the polyacrylate resins isdetermined by the nature and amount of the monomers employed. Theselection of the monomers can be made by the skilled worker with the aidof the following formula, which can be used to calculate approximatelythe glass transition temperatures of polyacrylate resins:${\frac{1}{TG} = {\sum\limits_{n}\frac{W_{n}}{{TG}_{n}}}};{{\sum\limits_{n}W_{n}} = 1}$

[0100] TG=Glass transition temperature of the polyacrylate resin

[0101] n=Number of different monomers copolymerized in the polyacrylateresin

[0102] W_(n)=Proportion by weight of the nth monomer

[0103] TG_(n)=Glass transition temperature of the homopolymer of the nthmonomer

[0104] Measures to control molecular weight (e.g. selection ofappropriate polymerization initiators, use of chain transfer agents,etc.) belong to the technical knowledge of the person of average skillin the art and do not need to be elucidated further here.

[0105] As hydroxy-functional binder component use is also made withparticular preference of polyester resins or alkyd resins which can beprepared by reacting (a) a cycloaliphatic or aliphatic polycarboxylicacid or a mixture of such polycarboxylic acids, (b) an aliphatic orcycloaliphatic polyol having more than two hydroxy groups in themolecule or a mixture of such polyols, (c) an aliphatic orcycloaliphatic diol or a mixture of such diols, and (d) an aliphaticlinear or branched saturated monocarboxylic acid or a mixture of suchmonocarboxylic acids in a molar ratio of (a): (b) : (c) :(d)=1.0:0.2-1.3:0.0-1.1:0.0-1.4, preferably 1.0:0.5-1.2:0.0-0.6:0.2-0.9,to give a polyester resin or alkyd resin.

[0106] Examples of component (a) are: hexahydrophthalic acid,1,4-cyclohexanedicarboxylic acid, endomethylenetetrahydrophthalic acid,oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid,pimelic acid, suberic acid, azelaic acid and sebacic acid.

[0107] Examples of component (b) are: pentaerythritol,trimethylolpropane, trimethylolethane and glycerol.

[0108] Examples of component (c) are: ethylene glycol, diethyleneglycol, propylene glycol, neopentyl glycol,2-methyl-2-propylpropane-1,3-diol, 2-ethyl-2-butylpropane-1,3-diol,2,2,4-trimethylpentane-1,5-diol, 2,2,5-trimethylhexane-1,6-diol,neopentyl glycol hydroxypivalate and dimethylolcyclohexane.

[0109] Examples of component (d) are: 2-ethylhexanoic acid, lauric acid,isooctanoic acid, isononanoic acid and monocarboxylic acid mixturesobtained from coconut oil or palm kernel oil.

[0110] The preparation of hydroxyl-bearing polyester resins and/or alkydresins is described, for example, in Ullmanns Encyklopädie dertechnischen Chemie, 3^(rd) edition, 14^(th) Volume, Urban &Schwarzenberg, Munich, Berlin, 1863, pages 80 to 89 and pages 99 to 105,and in the following books: Résines Alkydes-Polyesters by J. Bourry,Paris Verlag Dunod 1952, Alkyd Resins by C. R. Martens, ReinholdPublishing Corporation, New York 1961 and Alkyd Resin Technology by T.C. Patton, Interscience Publishers 1962.

[0111] Polyurethane-based protective coating materials are alsosuitable.

[0112] Suitable crosslinking agents are all compounds known per se, e.g.polyisocyanates, melamine resins, etc. In the case of this preferredprotective coating material, however, it is preferred for it to comprisethe crosslinking agents (2) and (3).

[0113] As component (2) use is made oftris(alkoxycarbonylamino)triazines of the formula

[0114] where R=methyl, butyl- . . . groups. It is likewise possible forderivatives of the compounds mentioned to be employed. For component (2)it is preferred to employ tris(alkoxycarbonylamino)triazines as aredescribed in U.S. Pat. No. 5,084,541.

[0115] The carbamate groups react preferentially with OH carriers and,specifically, with hydroxyl groups having as little steric hindrance aspossible. Amino groups cannot be crosslinked by thetris(alkoxycarbonylamino)triazine. Instead, there is elimination of thecarbalkoxy group.

[0116] Component (3) comprises as crosslinking agent(s) at least onepreferably non-blocked di- and/or polyisocyanate which may if desired bein solution or dispersion in one or more organic solvents, which may inturn be dilutable in water.

[0117] The polyisocyanate component comprises any desired organicpolyisocyanates having free isocyanate groups attached to aliphatic,cycloaliphatic, araliphatic and/or aromatic structures. It is preferredto employ polyisocyanates having from 2 to 5 isocyanate groups permolecule and having viscosities of from 100 to 2000 mPas (at 23° C.). Ifdesired, small amounts of organic solvent, preferably from 1 to 25% byweight based on pure polyisocyanate, can be added to the polyisocyanatesin order thus to improve the ease of incorporation of the isocyanateand, if desired, to reduce the viscosity of the polyisocyanate to avalue within the abovementioned ranges. Examples of solvents suitable asadditions to the polyisocyanates are ethoxyethyl propionate, butylacetate and the like.

[0118] Examples of suitable isocyanates are described, for example, in“Methoden der organischen Chemie”, Houben-Weyl, Volume 14/2, 4^(th)edition, Georg Thieme Verlag, Stuttgart 1963, page 61 to 70, and by W.Siefken, Liebigs Ann. Chem. (1949) 562, 75 to 136. Suitable, forexample, are the isocyanates referred to in connection with thedescription of the polyurethane resins (A2), and/or polyurethaneprepolymers which contain isocyanate groups, can be prepared by reactingpolyols with an excess of polyisocyanates and are preferably of lowviscosity.

[0119] It is also possible to employ polyisocyanates which containisocyanurate groups and/or biuret groups and/or allophanate groupsand/or urethane groups and/or urea groups and/or uretdione groups.Polyisocyanates containing urethane groups, for example, are obtained byreacting some of the isocyanate groups with polyols, such astrimethylolpropane and glycerol, for example.

[0120] It is preferred to employ aliphatic or cycloaliphaticpolyisocyanates, especially hexamethylene diisocyanate, dimerized andtrimerized hexamethylene diisocyanate, isophorone diisocyanate,2-isocyanatopropylcyclohexyl isocyanate, dicyclohexylmethane2,4′-diisocyanate or dicyclohexylmethane 4,4′-diisocyanate or mixturesof these polyisocyanates. Very particular preference is given to the useof mixtures of polyisocyanates, based on hexamethylene diisocyanate,which contain uretdione and/or isocyanurate groups and/or allophanategroups, as are formed by catalytic oligomerization of hexamethylenediisocyanate using appropriate catalysts. The polyisocyanate componentmay otherwise consist, in addition, of any desired mixtures of thepolyisocyanates mentioned by way of example.

[0121] The polyisocyanate component is employed in the coatingcompositions of the invention advantageously in an amount such that theratio of the hydroxyl groups of the binder (A) to the isocyanate groupsof the crosslinkers (2) and (3) lies between 1:2 and 2:1 and, withparticular preference, between 1:1.5 and 1.5:1.

[0122] The crosslinker mixture contains preferably from 1 to 99% byweight, with particular preference from 5 to 90% by weight oftris(alkoxycarbonylamino)triazine and, preferably, from 99 to 1% byweight and, with particular preference, from 95 to 10% by weight of freeisocyanate or of a mixture of free polyisocyanates.

[0123] In addition to the components stated, the protective coatingmaterial may also include light stabilizers, for example triazinecompounds. In addition, rheological agents may also be added.

[0124] In a preferred variant, the protective coating material is storedin the form of at least two separate components (I) and (II) which arenot mixed with one another until directly prior to application. It ispreferred for the tris(alkoxycarbonylamino)triazine in a mixture withthe hydroxy-functional binder to form component I and for the freepolyisocyanate to form component II of the protective coating materialor two-component clearcoat. In the case of a two-component system, theprotective coating material is designed such that a) one component (I)comprises a hydroxy-functional binder or a mixture of hydroxy-functionalbinders and tris(alkoxycarbonylamino)triazine, and b) the secondcomponent (II) comprises free isocyanate or a mixture of freepolyisocyanates. Preparation of the two components (I) and (II) takesplace by the customary methods from the individual constituents withstirring. Preparation of the protective coating material from components(I) and (II) takes place likewise by means of stirring or dispersingusing the commonly employed apparatus; for example, by means ofdissolvers or the like or by means of likewise customarily employed2-component metering and mixing units or by means of the process forpreparing aqueous 2-component polyurethane coating materials that isdescribed in DE-A-195 10 651, page 2, line 62 to page 4, line 5.

[0125] A preferred embodiment of the invention is characterized in thatthe decorative layer has a layer thickness in the range of 10 μm to 100μm and in that the protective layer has a layer thickness in the rangefrom 20 μm to 150 μm. It is advantageous, specifically, if the surfacerlayer has a layer thickness in the range of 50 μm to 80 μm, preferablyfrom 60 μm to 70 μm, if the decorative layer has a layer thickness inthe range of 15 μm to 17 μm, preferably from 15 μm to 16 μm, and if theprotective layer has a layer thickness in the range from 35 μm to 50 μm,preferably from 40 μm to 45 μm. This achieves on the one hand an optimumsurface quality and on the other hand an optimum decorative effect.

[0126] The surfacer layer may lie directly on the substrate material.Alternatively, between the substrate and the surfacer layer there may beat least one further layer, for example an anti-corrosive layer.

[0127] A preferred use of the invention comprises the substrate being ametal panel, preferably a motor vehicle bodywork panel. A further usecomprises the substrate being a plastics moulding, preferably a motorvehicle plastics moulding based on PVC.

[0128] The invention also relates to a process for preparing a substrateprovided with a multilayer coating, especially a motor vehicle bodyworkpanel or a motor vehicle plastics moulding, comprising the followingsubsequent process steps:

[0129] a) a crosslinkable powder coating material is applied to thesubstrate,

[0130] b) the powder coating material is dried and precrosslinked bymeans of irradiation or heating for from 1 minute to 10 minutes at atemperature in the range from 130 degrees C. to 240 degrees C.,

[0131] c) an aqueous decorative coating material is applied to the driedand precrosslinked powder coating material and is dried,

[0132] d) an aqueous protective coating material is applied to thedecorative coating,

[0133] e) the assembly of powder coating material, decorative coatingmaterial and protective coating material is baked and crosslinked at atemperature in the range from 120 degrees C. to 180 degrees C.

[0134] Prior to step a) it is possible, if desired, for anelectrodeposition coating operation to take place with subsequent bakingof the coating layer.

[0135] In detail it is preferred if the powder coating material is driedand precrosslinked for from 2 minutes to 6 minutes, preferably for from3 minutes to 4 minutes, at a temperature of from 180 degrees C. to 220degrees C., preferably by the passage of the substrate that has beenprovided with the powder coating material through an IR irradiationzone.

[0136] A coating which satisfies all requirements is obtained if theassembly of powder coating material, decorative coating material andprotective coating material is baked and crosslinked at a temperature inthe range from 130 degrees C. to 150 degrees C., preferably at 150degrees C.

[0137] An embodiment of the process of the invention that isparticularly advantageous in terms of energy consumption andenvironmental protection is characterized in that an aqueous decorativecoating material which is virtually free from organic solvents and anaqueous protective coating material which is virtually free from organicsolvents, or an aqueous transparent powder coating dispersion, are usedand in that the powder coating material, the decorative coating materialand the protective coating material are applied and baked in a coatingunit which is operated with circulating air.

[0138] The invention is elucidated further in the text below usingexamples.

EXAMPLE 1 Powder Coating Material for the Surfacer layer EXAMPLE 1Preparing a Powder Coating Material

[0139] Premixing

[0140] The following items are weighed in: 120.30 kg 20.1% Epoxy resin228.30 kg 38.1% Polyester 121.80 kg 20.3% TiO₂ 118.80 kg 19.8% Filler 2.40 kg 0.4% Benzoin  2.40 kg 0.4% Wax  6.00 kg 1.0% Levelling additive600.00 kg 100.0%

[0141] The components are subsequently mixed in an overhead mixer for 5minutes.

[0142] Extrusion

[0143] The premix is supplied to the extruder, in this case asingle-screw extruder of type Buss PCS 100.

[0144] In other words, extrudate is rolled as a sheet on a cooling belt,cooled, fractionated and recovered as chips.

[0145] Milling and Classifying

[0146] The chips are supplied to a classifier mill of type ACM 40 andare classified in-line with a cyclone classifier.

[0147] The resulting coarse fraction G1 is discharged using a cellularwheel sluice and constitutes the useful material. The fine fraction isdeposited by the stream of air on an absolute filter (surface filtermade from PE needlefelt) and likewise discharged via a cellular wheelsluice. Particle size distribution: x₁₀>10 μm; x₉₀<40 μm.

EXAMPLE 2 Decorative Coating Materials for the Decorative Layer EXAMPLE2.1

[0148] A. A reaction vessel was charged with 22 parts by weight ofwater, 2 parts by weight of Solvesso 200 (C₁₀-C₁₃ aromatics mixture) and1 part by weight of butyl glycol. With stirring, 30 parts by weight ofAcronal 290 D (aqueous dispersion, solids content 50.0%) were added.

[0149] B. A mixture of 7.6 parts by weight of water and 2 parts byweight of Viscalex HV 30 (solids content 30.6%) was added slowly to themixture obtained in A.

[0150] The pH of the resulting mixture was adjusted to 8.0 withdimethylethanolamine (DMEA).

[0151] C. In a separate mixer, a mixture of 5 parts by weight ofaluminium flakes and 5 parts by weight of butyl glycol was stirred untilsmooth.

[0152] With vigorous stirring, the aluminium suspension obtained in C.was added in portions to the mixture obtained in B.

[0153] The viscosity of the resulting coating material was adjusted to110 mPas using 25 parts by weight of water. The solids content was18.85%.

EXAMPLE 2.2

[0154] A. A reaction vessel was charged with 22 parts by weight ofwater, 2 parts by weight of Solvesso 200 (C₁₀-C₁₃ aromatics mixture) and1 part by weight of butyl glycol. With stirring, 25 parts by weight ofAcronal 290 D (aqueous dispersion, solids content 50.0%) were added.

[0155] B. A mixture of 7.6 parts by weight of water and 2 parts byweight of Viscalex HV 30 (solids content 30.6%) was added slowly to themixture obtained in A.

[0156] The pH of the resulting mixture was adjusted to 8.0 with 0.4 partby weight of dimethylethanolamine (DMEA).

[0157] C. In a separate mixer, a mixture of 5 parts by weight ofaluminium flakes and 5 parts by weight of butyl glycol was stirred untilsmooth.

[0158] D. In a further separate mixer, 5 parts by weight of glycidylmethacrylate-dodecanedioic acid were dispersed in 25 parts by weight ofwater and milled to a particle size of less than 5 μm.

[0159] The mixture obtained in B was incorporated with vigorous stirringinto the dispersion obtained in D.

[0160] The aluminium suspension obtained in C was then added in portionsto the resulting mixture.

[0161] The viscosity of the resulting coating material was adjusted to110 mPas using 25 parts by weight of water. The solids content was18.35%.

Example 2.3

[0162] A coating formulation was prepared by the procedure described inExample 2.2, with the exception that in step D 10 parts by weight ofglycidyl methacrylate/dodecanedioic acid were dispersed in 20 parts byweight of water.

[0163] The solids content was 20.35%.

EXAMPLE 2.4

[0164] A. A reaction vessel was charged with 22 parts by weight ofwater, 2 parts by weight of Solvesso 200 (C₁₀-C₁₃ aromatics mixture) and1 part by weight of butyl glycol. With stirring, 30 parts by weight ofAcronal 290 D (aqueous dispersion, solids content 50.0%) were added.

[0165] B. A mixture of 7.6 parts by weight of water and 2 parts byweight of Viscalex HV 30 (solids content 30.6%) was added slowly to themixture obtained in A.

[0166] The pH of the resulting mixture was adjusted to 8.0 with 0.4 partby weight of dimethylethanolamine (DMEA).

[0167] C. In a separate mixer, a mixture of 5 parts by weight ofaluminium flakes and 5 parts by weight of butyl glycol was stirred untilsmooth.

[0168] D. In a further separate mixer, 10 parts by weight of a polyesterobtained from 9.8% by weight of neopentyl glycol, 6.2% by weight ofhexahydrophthalic acid, 22.9% by weight of Pripol (commercial productfrom Unichema), 11.1% by weight of hexanediol and 2.0% by weight ofxylene as solvent, and 2.2 parts by weight of melamine Cymel 303(Cyanamid) were dispersed in 12.8 parts by weight of water.

[0169] The mixture obtained in B was incorporated with vigorous stirringinto the dispersion obtained in D.

[0170] The aluminium suspension obtained in C was then added in portionsto the resulting mixture.

[0171] The solids content of the coating material was 26.83%.

EXAMPLE 2.5

[0172] A. A reaction vessel was charged with 22 parts by weight ofwater, 2 parts by weight of Lusolvan FBH (commercial product from BASFAG, Ludwigshafen) and 1 part by weight of butyl glycol. With stirring,30 parts by weight of Acronal 290 D (aqueous dispersion, solids content50.0%) were added.

[0173] B. A mixture of 7.6 parts by weight of water and 2 parts byweight of Viscalex HV 30 (solids content 30.6%) was added slowly to themixture obtained in A.

[0174] The pH of the resulting mixture was adjusted to 8.0 withdimethylethanolamine (DMEA).

[0175] C. 30 parts by weight of an Irgazine red DPP BO paste (pigmentcontent 43.2% by weight) were added to the mixture obtained in step B,and the resulting mixture was stirred until smooth.

[0176] The viscosity of the resulting coating material was adjusted to110 mpas with 5 parts by weight of water.

EXAMPLE 2.6

[0177] A. A reaction vessel was charged with 22 parts by weight ofwater, 2 parts by weight of Lusolvan FBH (commercial product of BASF AG,Ludwigshafen) and 1 part by weight of butyl glycol. With stirring, 25parts by weight of Acronal 290 D (aqueous dispersion, solids content50.0%) were added.

[0178] B. A mixture of 7.6 parts by weight of water and 2 parts byweight of Viscalex HV 30 (solids content 30.6%) was added slowly to themixture obtained in A.

[0179] The pH of the resulting mixture was adjusted to 8.0 withdimethylethanolamine (DMEA).

[0180] C. In a separate mixer, 28.79 parts by weight of an Irgazine redDPP BO paste (pigment content 43.2% by weight), 1.17 parts by weight ofDisperbyk 190 (dispersion auxiliary) and 0.03 part by weight of thecopolymer employed in step B were dispersed and ground to a particlesize of less than 5 μm.

[0181] D. In a further separate mixer, 5 parts by weight of glycidylmethacrylate-dodecanedioic acid were dispersed in 25 parts by weight ofwater and milled to a particle size of less than 5 μm.

[0182] The mixture obtained in B was incorporated with vigorous stirringinto the dispersion obtained in D.

[0183] The pigment paste obtained in C was then added in portions to theresulting mixture.

[0184] The solids content was 28.06%.

EXAMPLE 2.7

[0185] The procedure described in Example 2.6 was repeated except thatin step A 20 parts by weight of the acrylate dispersion and in step D 10parts by weight of glycidyl methacrylate/dodecanedioic acid wereemployed.

EXAMPLE 2.8

[0186] A. A reaction vessel was charged with 22 parts by weight ofwater, 2 parts by weight of Lusolvan FBH (commercial product of BASF AG,Ludwigshafen) and 1 part by weight of butyl glycol. With stirring, 15parts by weight of Acronal 290 D (aqueous dispersion, solids content50.0%) acrylate dispersion were added.

[0187] B. A mixture of 7.6 parts by weight of water and 2 parts byweight of Viscalex HV 30 (solids content 30.6%) was added slowly to themixture obtained in A.

[0188] The pH of the resulting mixture was adjusted to 8.0 withdimethylethanolamine (DMEA).

[0189] C. In a separate mixer, 28.79 parts by weight of an Irgazine redDPP BO paste (pigment content 43.2% by weight), 1.17 parts by weight ofDisperbyk 190 and 0.03 part by weight of the copolymer employed in stepB were dispersed and ground to a particle size of less than 5 μm.

[0190] D. In a further separate mixer, 10 parts by weight of a polyesterobtained from 9.8% by weight of neopentyl glycol, 6.2% by weight ofhexahydrophthalic acid, 22.9% by weight of Pripol (commercial productfrom Unichema), 11.1% by weight of hexanediol and 2.0% by weight ofxylene as solvent, and 2.2 parts by weight of melamine Cymel 303(Cyanamid) were dispersed in 12.8 parts by weight of water.

[0191] The mixture obtained in B was then incorporated with vigorousstirring into the dispersion obtained in D. The pigment preparationprepared in step B was then incorporated by stirring.

[0192] The solids content was 29.04%.

EXAMPLE 3 Protective Coating Materials for the Protective Layer EXAMPLE3.1

[0193] A. Preparing an acrylate resin: 21.1 parts of xylene are chargedto a vessel and heated to 130° C. Into the initial charge over 4 h at130° C. by way of two separate feed vessels there are metered:initiator: 4.5 parts of TBPEH (tert-butyl perethylhexanoate) mixed with4.86 parts of xylene; and monomers: 10.78 parts of methyl methacrylate,25.5 parts of n-butyl methacrylate, 17.39 parts of styrene and 23.95parts of glycidyl methacrylate. The batch is then heated to 180° C. andthe solvent is stripped off under reduced pressure<100 mbar.

[0194] B. Preparing a transparent powder coating material: 77.5 parts ofacrylate resin, 18.8 parts of dodecanedicarboxylic acid (see hardener),2 parts of Tinuvin 1130 (UV absorber), 0.9 part of Tinuvin 144 (HALS),0.4 part of Additol XL 490 (levelling agent) and 0.4 part of benzoin(degassing agent) are intimately mixed on a Henschel fluid mixer,extruded on a BUSS PLK 46 extruder, milled on a Hosokawa ACM 2 mill andscreened off over a 125 μm sieve.

[0195] C. Preparing a dispersion: 0.6 part of Troykyd D777 (antifoam),0.6 part of Orotan 731 K (dispersing auxiliary), 0.06 part of SurfinolTMN 6 (wetting agent) and 16.5 parts of RM8 (Rohm & Haas, nonionicassociative thickener based on polyurethane) are dispersed in 400 partsof deionized water. Then 94 parts of the transparent powder coatingmaterial are incorporated in small portions with stirring. Subsequently,a further 0.6 part of Troykyd D777, 0.6 part of Orotan 731 K, 0.06 partof Surfinol TMN 6 and 16.5 parts of RM8 are incorporated by dispersion.Finally, 94 parts of the transparent powder coating material areincorporated in small portions with stirring. The material is milled ina sand mill for 3.5 h.

[0196] The finally measured average particle size is 4 μm. The materialis filtered through a 50 μm filter and finally 0.05% of Byk 345(levelling agent) is added.

[0197] D. Applying the dispersion: the slurry is applied by means of acup gun to steel panels coated with aqueous basecoat. The panel isflashed off at room temperature for 5 minutes and at 60° C. for 5minutes. Subsequently, the panel is baked for 30 minutes at atemperature of 140° C. With a layer thickness of 40 μm a highly glossyclearcoat film with MEK resistance (>100 double strokes) is produced.The clearcoat film exhibits good condensation resistance.

Example 3.2

[0198] 3.2.1. Preparing Binder Solutions

[0199] A: Acrylate resin A

[0200] 899 g of a fraction of aromatic hydrocarbons having a boilingrange of 158° C.-172° C. are weighed into a laboratory reactor having auseful volume of 4 l and equipped with a stirrer, two dropping funnelsfor the monomer mixture and initiator solution respectively, nitrogeninlet pipe, thermometer and reflux condenser. The solvent is heated to140° C. After the solvent has reached 140° C., a monomer mixture of 727g of n-butyl methacrylate, 148 g of cyclohexyl methacrylate, 148 g ofstyrene, 445 g of 4-hydroxybutyl acrylate and 15 g of acrylic acid ismetered over the course of 4 hours, and an initiator solution of 29 g oft-butyl perethylhexanoate in 89 g of the aromatic solvent describedabove, over the course of 4.5 hours, into the reactor at a uniform rate.The metered addition of the monomer mixture and the initiator solutionis commenced simultaneously. Following the end of the metered additionof an initiator, the reaction mixture is held at 140° C. for two hoursmore and then cooled. The resulting polymer solution has a solidscontent of 62% (determined in a convection oven at 130° C. for 1 h), anacid number of 9 and a viscosity of 21 dPas (measured on a 60% strengthsolution of the polymer solution in the aromatic solvent describedabove, using an ICI plate/cone viscometer at 230° C.).

[0201] B: Acrylate resin B

[0202] 897 g of a fraction of aromatic hydrocarbons having a boilingrange of 158° C.-172° C. are weighed into a laboratory reactor having auseful volume of 4 l and equipped with a stirrer, two dropping funnelsfor the monomer mixture and initiator solution respectively, nitrogeninlet pipe, thermometer and reflux condenser. The solvent is heated to140° C. After the solvent has reached 140° C., a monomer mixture of 487g of t-butyl acrylate, 215 g of n-butyl methacrylate, 143 g of styrene,572 g of hydroxypropyl methacrylate and 14 g of acrylic acid is meteredover the course of 4 hours, and an initiator solution of 86 g of t-butylperethylhexanoate in 86 g of the aromatic solvent described above, overthe course of 4.5 hours, into the reactor at a uniform rate. The meteredaddition of the monomer mixture and the initiator solution is commencedsimultaneously. Following the end of the metered addition of aninitiator, the reaction mixture is held at 140° C. for two hours moreand then cooled. The resulting polymer solution has a solids content of62% (determined in a convection oven at 130° C. for 1 h), an acid numberof 10 and a viscosity of 23 dPas (measured on a 60% strength solution ofthe polymer solution in the aromatic solvent described above, using anICI plate/cone viscometer at 23° C.).

[0203] C: Alkyd resin C

[0204] 1330 g of hexahydrophthalic anhydride, 752 g of1,1,1-trimethylolpropane, 249 g of 1,4-dimethylolcyclohexane, 204 g ofhexane-1,6-diol, 136 g of isononanoic acid (as an isomer mixture of3,3,5-trimethylhexanoic acid and 3,5,5-trimethylhexanoic acid) and 75 gof xylene as entrainer are weighed into a laboratory reactor having auseful volume of 4 l and equipped with a stirrer, water separator,reflux condenser, nitrogen inlet pipe and thermometer. The waterseparator is filled with xylene. The contents of the reactor are heatedover the course of 8 hours to 210° C. at a level such that uniformreflux of the entrainer results. The contents of the reactor are held at210° C. until an acid number of 17.1 and a viscosity of 15 dpas,measured on a 60% strength solution of the reaction mixture in thearomatic solvent described for the acrylate resins A and B, have beenreached. The batch is then cooled to 140° C. and the contents of thereactor are diluted with an amount of the stated aromatic solvent suchas to give a nonvolatiles content of 61% (determined in a convectionoven at 130° C. for 60 minutes). The alkyd resin solution prepared inthis way has an acid number of 17.1 and a viscosity of 15 dPas (measuredon an ICI plate/cone viscometer at 230° C.).

[0205] 3.2.2 Preparing the Two-Component Clearcoats

[0206] A: Component 1

[0207] Component 1 of the two-component clearcoats is prepared byweighing in the binder solution and then adding, with stirring, theamounts indicated in Table 1 of triazine crosslinker, solvent, UVabsorber, free-radical scavenger and levelling agent and stirring thesecomponents in thoroughly. The amounts given in this table and thesubsequent tables are to be understood as amounts by weight. TABLE 1Comp. 1a Comp. 1b Comp. 1c Comp. 1d Comp. 1e Comp. 1f Acrylate resin A79.6 55.0 Acrylate resin B 62.8 50.0 Alkyd resin C 72.0 62.0 Triazinecrosslinker 13 12.8 10.0 US 5084541 Tinuvin 400 1.3 1.3 1.0 1.0 Tinuvin123 1.0 1.0 1.5 1.5 Tinuvin 384 1.2 1.2 Tinuvin 292 1.0 1.0 Silicone oilsolution 2.5 2.5 2.5 2.5 3.0 3.0 Butyl diglycol acetate 4.0 4.0 10.010.0 9.0 9.0 Butyl glycol acetate 4.0 4.0 8.0 8.0 5.5 5.5 Methoxypropylacetate 3.0 3.6 8.0 8.4 Solvent naphtha 5.1 5.1 Butyl acetate 4.6 15.65.8 5.8 3.2 3.2

[0208] B: Component 2

[0209] Component 2 consists of a solution of customary commercialisocyanurate trimers in an appropriate solvent. It is prepared bystirring the solvent into the supply form of the isocyanurates inaccordance with Table 2. TABLE 2 Component 2a Component 2b DesmodurZ4470 63.5 26.5 Tolonate HDT 90 24.8 Basonat HI 190 B/S 61.8 Solventnaphtha 5.85 Butyl acetate 5.85

[0210] C: Preparing the clearcoats

[0211] The clearcoats are prepared by mixing components 1 and 2 in theproportions indicated in Table 3 and applying the mixture immediatelyafter mixing. Alternatively, it is also possible to carry outapplication using special two-component units which are known to theperson of average skill in the art and hence need not be described inany more detail here. Table 3 also includes properties of theclearcoats, which elucidate the invention. TABLE 3 Clearcoat 1 Clearcoat2 Clearcoat 3 Clearcoat 4 Clearcoat 5 Clearcoat 6 Comp. 1a 73.9 Comp. 1b93.5 Comp. 1c 77.0 Comp. 1d 91.0 Comp. 1e 76.7 Comp. 1f 86.7 Comp. 2a26.1 6.5 Comp. 2b 23.0 9.0 23.3 13.3 Scratch resistance poor good poorgood poor good JV (Rating) ⁺1)  4.0  4.0  4.5  4.5  3.0  3.0 Stonechipping poor good poor good poor good

EXAMPLE 4 Preparing a Substrate Provided With a Multilayer Coating.

[0212] Using 180 grade abrasive paper, abrasion scars are producedartificially (cf. FIG. 1) on a metal panel made of material common inmotor vehicle bodywork construction. A powder coating material assurfacer in accordance with Example 1 was first of all applied to thissurface-defective panel by means of electrostatic adhesion. The panelprovided with the powder surfacer surfacer (FIG. 2) was thenIR-irradiated for 4 minutes, in the course of which a temperature ofabout 200° C. was established. At this point, the powder coatingsurfacer was melted and crosslinked. In the present example, it was notpossible to detect any residual reactivity from the crosslinkingreaction of polyester resin and epoxy resin by DSC examination. Avirtually smooth filled surface was the result. Following the IRirradiation, a decorative coating material in accordance with Example2.1 was applied with the customary spraying technique followed by adrying procedure for film formation. A transparent powder coatingdispersion in accordance with Example 3.1 was sprayed onto theincipiently dried decorative coating material. Finally, the panel coatedin this way was subjected to a baking process stage at 150° C. for 20minutes.

[0213] The layer thicknesses for the finished multilayer coating were asfollows: surfacer layer: 60 μm, decorative layer: 16 μm, protectivelayer: 40 μm. The surface of the multilayer coating gave a flawlessvisual impression. In particular, no signs of the surface defects of themetal panel were in evidence. The stone-chip resistance in accordancewith VDA621-427 with 2×500 g of steel chips and 2 bar air pressure gavea KW1.

[0214] A second metal panel was coated with an aqueous surfacer forcomparison (FIG. 3). Comparison of FIGS. 2 and 3 shows that the coatingoperation of the invention using powder coating material, in accordancewith FIG. 2, gives a substantially smoother surface than the coatingwith aqueous surfacer, in accordance with FIG. 3.

[0215] Perthometric measurement of the powder coating surfacer showscomplete levelling of the abrasion scars (FIG. 2), whereas an aqueoussurfacer, applied conventionally at 35 μm, leaves behind considerablemarks (FIG. 3).

[0216]FIG. 4 depicts by way of example the procedure of coating avehicle body.

[0217] The body to be coated passes via the entry 1 into thepretreatment stage 2. This is followed by electrodeposition coating 3and the baking 4 of the electrodeposition coat. In stage 5 preparationtakes place for coating with powder coating material (stage 6). In stage7 drying is carried out with IR irradiation. This is followed by thecooling stage 8. The powder coating material is applied to the powdercoat in stage 9. Following passage through the intermediate drying stage10 a protective coat is applied in stage 11 and then is baked in stage12. The body is transported out of the unit via the exit 13.

1. A process for preparing a substrate provided with a multilayer coating, wherein the substrate is selected from the group consisting of a motor vehicle bodywork panel and a motor vehicle plastics moulding, comprising the following process steps: a) applying a surfacer layer comprising a crosslinkable powder coating material to the substrate, wherein the surfacer layer has a layer thickness in the range from 30 μm to 250 μm; b) drying the powder coating material and precrosslinking by means of irradiation or heating from 1 minute to 10 minutes at a temperature in the range from 130° C. to 240° C.; c) applying an aqueous decorative coating material to the dried and precrosslinked powder coating material and drying the aqueous decorative coating material, wherein the aqueous decorative coating material comprises a binder selected from the group consisting of acrylate resins, carboxyl-,epoxy-, and hydroxyl-containing binders and mixtures thereof and comprising a crosslinker selected from the group consisting of isocyanates, amino resins, tris(alkoxy carbonylamino) triazine, and mixtures thereof; d) applying an aqueous protective coating material to the decorative coating material, wherein the aqueous protective coating is selected from the group consisting of one-component clearcoats, two-component clearcoats, and transparent powder coating materials; and e) baking and crosslinking the assembly of the surfacer layer, the decorative coating material, and the protective coating material at a temperature in the range from 120° C. to 180° C.
 2. The process of claim 1, wherein the surfacer layer is dried and precrosslinked from 2 minutes to 6 minutes at a temperature of from 180° C. to 220° C.
 3. The process of claim 1, wherein the assembly of surfacer layer, decorative coating material, and protective coating material is baked and crosslinked at a temperature in the range from 130° C. to 150° C.
 4. The process of claim 2, wherein the assembly of surfacer layer, decorative coating material, and protective coating material is baked and crosslinked at a temperature in the range from 130° C. to 150° C.
 5. The process of claim 1, wherein the aqueous decorative coating material is virtually free from organic solvents; the aqueous protective coating is selected from the group consisting of an aqueous protective coating material that is virtually free from organic solvents and an aqueous transparent powder coating dispersion; and wherein the surfacer layer the decorative coating material, and the protective coating material are applied and baked in a coating unit that is operated with circulating air.
 6. The process of claim 1, wherein the surfacer layer is dried and precrosslinked for from 2 minutes to 6 minutes, at a temperature of from 180° C. to 220° C., by the passage of the substrate that has been provided with a powder coating material through an IR irradiation zone.
 7. The process of claim 1, wherein the decorative layer has a layer thickness in the range of 10 μm to 100 μm and in the protective layer has a layer thickness in the range from 20 μm to 150 μm.
 8. The process of claim 1, wherein the surfacer layer has a layer thickness in the range of 50 μm to 80 μm, the decorative layer has a layer thickness in the range of 15 μm to 17 μm, and the protective layer has a layer thickness in the range from 35 μm to 50 μm.
 9. The process of claim 1, wherein the surfacer layer lies directly on the substrate material.
 10. The process of claim 1, wherein the substrate is a metal panel.
 11. The process of claim 1, wherein the substrate is a plastics moulding.
 12. The process of claim 1, wherein the surfacer layer has a layer thickness in the range from 60 μm to 70 μm, the decorative layer has a layer thickness in the range from 15 μm to 16 μm, and the protective layer has a layer thickness in the range from 40 μm 45 μm.
 13. The process of claim 1, wherein the substrate is a motor vehicle bodywork panel.
 14. The process of claim 1, wherein the substrate is a motor vehicle plastics moulding based on sheet molded compound. 